1. Field of the Invention
This invention relates to power distribution units and more particularly relates to branch protection within power distribution units.
2. Description of the Related Art
Power distribution units (“PDUs”) are used to distribute electric power for electrically intensive applications such as computer data centers, industrial equipment, electric motors, and the like. PDUs typically have a safe grounding system and provide overcurrent protection using circuit breakers.
Including circuit breakers in a PDU, however, has several negative effects. For example, using circuit breakers increases the cost of the PDU. If a separate circuit breaker is used for each outlet of a PDU, the circuit breakers increase the cost of the PDU dramatically.
Additionally, if a circuit breaker trips, it must be physically reset, even after an overcurrent fault has been remedied. This means that once a circuit breaker trips, the outlets protected by the circuit breaker cannot be used again until someone arrives on location and resets the circuit breaker. This can extend power interruptions long after the overcurrent fault no longer exists.
Circuit breakers also generate heat. PDUs are often enclosed and have no fans or other cooling systems. Including circuit breakers in the enclosed, fanless environment of a PDU increases the operating temperature of the PDU dramatically. High temperatures can affect the operation of a PDU itself, increase temperatures of other equipment around the PDU, and pose a safety threat.
Circuit breakers can also be rather bulky. Including circuit breakers in a PDU increases the size of the PDU. Larger PDUs require more material to manufacture, increasing material costs. PDUs that are larger are also less flexible in use, requiring more space in what are often tight quarters.
Further, circuit breakers can take a long time to trip during overcurrent conditions. Extended periods of overcurrent conditions can cause output voltages to sag and may have other negative effects on an electrical load that receives power from the PDU. Using circuit breakers for PDU branch protection trades cost, convenience, heat, and size for safety.